java - NullPointerException SQLiteAssetHelper

Question

我正在尝试从数据库中获取信息列表并将其显示到自定义 ListView 中。我已经有了 DatabaseHelper、Fragment 和 Adapter 设置。以下是我收到的错误:

04-29 13:36:52.539: E/AndroidRuntime(8135): FATAL EXCEPTION: main
04-29 13:36:52.539: E/AndroidRuntime(8135): java.lang.NullPointerException
04-29 13:36:52.539: E/AndroidRuntime(8135):     at com.readystatesoftware.sqliteasset.SQLiteAssetHelper.<init>(SQLiteAssetHelper.java:110)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at com.readystatesoftware.sqliteasset.SQLiteAssetHelper.<init>(SQLiteAssetHelper.java:130)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at com.rcd.mypr.Workouts.WorkoutsDatabaseHelper.<init>(WorkoutsDatabaseHelper.java:35)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at com.rcd.mypr.Workouts.WorkoutsFragment.onCreateView(WorkoutsFragment.java:36)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:828)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1032)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at android.app.BackStackRecord.run(BackStackRecord.java:622)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1382)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at android.app.FragmentManagerImpl$1.run(FragmentManager.java:426)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at android.os.Handler.handleCallback(Handler.java:605)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at android.os.Handler.dispatchMessage(Handler.java:92)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at android.os.Looper.loop(Looper.java:137)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at android.app.ActivityThread.main(ActivityThread.java:4424)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at java.lang.reflect.Method.invokeNative(Native Method)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at java.lang.reflect.Method.invoke(Method.java:511)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
04-29 13:36:52.539: E/AndroidRuntime(8135):     at dalvik.system.NativeStart.main(Native Method)

这是我的 WorkoutsDatabaseHelper.java

package com.rcd.mypr.Workouts;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

import com.readystatesoftware.sqliteasset.SQLiteAssetHelper;

public class WorkoutsDatabaseHelper extends SQLiteAssetHelper {


    // All Static variables
    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "workoutsDatabase.sqlite";
    private static final String WORKOUTS_TABLE = "workouts";

    // Workouts Table Columns names
    private static final String KEY_ID = "_id";
    private static final String KEY_WORKOUT_NAME = "workout_name";
    private static final String KEY_HERO_LAST_NAME = "hero_last_name";
    private static final String KEY_HERO_FIRST_NAME = "hero_first_name";
    private static final String KEY_HERO_MIDDLE_NAME = "hero_middle_name";
    private static final String KEY_HERO_DESCRIPTION = "hero_description";
    private static final String KEY_DATE_ADDED = "date_added";
    private static final String KEY_WORKOUT = "workout";
    private static final String KEY_MEASUREMENT = "measurement";
    private static final String KEY_PHOTO = "photo";



    public WorkoutsDatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    public Cursor getWorkoutNames() {

        SQLiteDatabase db = getReadableDatabase();
        Cursor cursor = db.query(WORKOUTS_TABLE, new String[] {"_id", "workout_name"}, null, null, null,
                null, KEY_WORKOUT_NAME + " ASC");
        return cursor;

    }


 }

最后，这是我的 WorkoutsFragment.java

package com.rcd.mypr.Workouts;

import android.app.Fragment;
import android.content.Context;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.widget.SimpleCursorAdapter;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;

import com.rcd.mypr.R;


public class WorkoutsFragment extends Fragment {

    WorkoutsDatabaseHelper db;
    SimpleCursorAdapter adapter;
    ListView listContent;
    private int position;
    Cursor cursor;
    private Context mContext;
    WorkoutsAdapter workoutsAdapter;

    public WorkoutsFragment(){}


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        db = new WorkoutsDatabaseHelper(mContext);
        mContext = getActivity();
        View rootView = inflater.inflate(R.layout.activity_workouts, container, false);

        listContent = (ListView) rootView.findViewById(android.R.id.list);

        // Create the Adapter
        workoutsAdapter = new WorkoutsAdapter(mContext, cursor);

        // Set the adapter to ListView
        listContent.setAdapter(workoutsAdapter);
        return rootView;
    }



    private void initViews(){
        //Typeface tf = Typeface.createFromAsset(mContext.getAssets(),"Roboto-Light.ttf");
    }

    private void addItemsToList(){
        Cursor cursor = db.getWorkoutNames();
        Log.d("history.java", "finished Cursor cursor = db.getAllLogs();");
        String[] from = {"_id", "workouts_name"};
        int[] to = {R.id.tv_id, R.id.tv_label};
        adapter = new SimpleCursorAdapter(mContext, R.layout.single_item, cursor, from, to, 0);
        listContent.setAdapter(adapter);

    }

    public void onResume(){
        super.onResume();
        workoutsAdapter = new WorkoutsAdapter(mContext, cursor);
        listContent.setAdapter(workoutsAdapter);
    }


}

如果您还需要查看其他内容，请告诉我。

Answer 1

错误出现在 Fragment 的 onCreateView() 方法中。您可以使用 null Context 初始化您的 WorkoutsDatabaseHelper。

    db = new WorkoutsDatabaseHelper(mContext);
    mContext = getActivity();

交换这两行并重试...